Public radio telephone networks, for example cellular telephone networks, are an established feature of many telecommunication systems. Typically, they provide to a user services that are available to conventional land line subscribers, but with the advantage of geographical mobility. In a cellular system, for example, a telecommunications service is provided over a wide geographic area by dividing the area into a number of cells. The geographic area can extend over national borders for example in the case of the Global System for Mobiles (GSM). Each cell has a base station which provides a radio signalling channel, and audio and data channels. The radio signalling channels are utilised to page radio telephones within a base station's coverage area, and to place calls to other radio telephones either inside or outside the base station area, or onto another network such as the Public Switched Telephone Network (PSTN).
Once a radio telephone has successfully placed or received a call, an audio or data radio channel is set up with the base station, and communication between the base station and radio telephone occurs over that audio or data channel. The radio telephone may also receive control or timing information over the signalling channel whilst a call is in progress. If a radio telephone leaves the cell during a call and enters another cell, the radio telephone hands over the call to an available audio or data channel in the new cell. Similarly, if no call is in progress a control message is sent over the signalling channel such that the radio telephone logs onto a base station associated with the new cell. In this manner mobile communication over a wide geographical area is possible.
Facilities offered by radio telephone networks such as the GSM network extend to facsimile transmissions and digital data transmission as well as speech services. In addition to these conventional telecommunication services, supplementary services may also be provided. In the GSM system for example, such a supplementary system is the Short Message Service (SMS) which is supported by the GSM network and is optional for GSM network operators. Short messages are alphanumeric text messages of up to 160 characters in length for GSM, which can be sent over the radio telephone network to and from a radio telephone. In this context the radio telephone is operating beyond its conventional telephony functions and it is convenient to refer to it generically as a mobile station.
An example of a mobile station operable for the GSM network and capable of supporting SMS is the NOKIA.RTM. 2110 radio telephone 100 shown in FIG. 1 and manufactured by Nokia Mobile Phones Limited. The operation of a NOKIA.RTM. 2110 for receiving and sending SMS messages is described in pages 28 to 32 of the NOKIA.RTM. 2110 User's guide issue 3. The memories associated with the NOKIA.RTM. 2110 are its internal memory and Subscriber Identity Module (SIM) card memory. However, these memories are limited such that the SIM card typically has space for less than ten messages and the phone or mobile station memory has space for five messages of maximum length. When a SMS message has been received, the mobile station displays a message to that effect and the user can either read the message straight away or store the message for reading later. The currently active message can also be deleted by the user. A user may also select and read previously stored messages, erase them or reply to them. Additionally, a user may edit the currently active message or forward it to another telephone number.
The manner in which alphabet characters are input to the NOKIA.RTM. 2110 will now be described with reference to FIG. 1 of the drawings. To send a message the user has to key in the characters using the alphanumeric key pad 110 provided on the NOKIA.RTM. 2110. For alphabet characters this involves entering an "alpha" mode by pressing a special function key 108a labelled "ABC" and then pressing the alphanumeric key 110 labelled with the desired letter a number of times corresponding to the placement division of the desired character on that key. This is a very laborious, time consuming and awkward process. A complete description of the method of inputting non-numeric characters to the NOKIA.RTM. 2110 is provided in pages 24 to 26 of the User's guide issue 3. Having input the text message via the key pad the user then instructs the phone to send the message and inputs the phone number of the intended recipient of the message. Optionally, the message can be stored in one of the message memories (internal memory or SIM card memory) of the phone and despatched later.